The subject matter of the present invention relates to a setting tool used in association with downhole apparatus disposed in a wellbore, and more particularly, to a setting tool which is adapted for setting an anchor or other downhole device in response to the hydrostatic pressure of an annulus fluid disposed in the annulus section of a wellbore, the setting tool moving a piston and forcing oil to transfer from an oil chamber to an air chamber through an oil metering orifice in response to the hydrostatic pressure of the annulus fluid, the orifice including an apparatus for selectively allowing the oil to transfer through orifice in response to a current delivered to the apparatus from a user at the well surface.
In the life of every oil well, anchoring of various pieces of downhole equipment is commonplace. Common types of anchored downhole equipment include permanent production packers, testing or retrievable packers, bridge plugs, cement retainers, pressure gauge/instrument hangers, and perforating guns. These devices are anchored in a well to the casing by expanding slips, the slips being expanded by relative opposing motion of a mandrel to a fixed point in the device. The relative motion, normally compression, moves slips radially outward. The slips have either hardened wicker teeth or carbide inserts to bite into the casing, and hold the anchored device stationary. The anchored devices can be actuated in several ways; for example, by rotary motion and tension of drill pipe/tubing, compressive set down weight accomplished by slacking of pipe/tubing weight, or by a setting tool run on electric cable which creates its own relative motion, independent of outside mechanical means.
The subject invention is such a setting tool. There are many kinds of setting tools for downhole equipment. Most are unique to the type of downhole equipment that they set. For electric wireline conveyed setting tools, the most common kind of setting tool is activated by electric current conveyed through the wireline, the electric current igniting a flammable solid in the tool. A gas is created by the burning of the flammable solid, the pressure of the gas causing the setting tool to linearly expand, the expansion causing relative opposing axial motion to occur between the setting tool outer housing and its inner mandrel. The relative motion compresses an anchor/packer and wedges the slips of the anchor/packer against a wellbore casing wall. When the wedging force of the slips against the casing reaches a predetermined value, a tension sleeve or stud, which connects the setting tool to an anchored device, breaks. The anchored device and setting tool separate, leaving the anchored device downhole, allowing the setting tool to be retrieved to the surface via the wireline cable. When setting packers with elastomeric sealing elements, it is desirable to set at a slower rate of speed. This allows the elastomeric sealing elements time to expand and to conform to new shapes without damage, thereby assuring reliability. Wireline setting tools normally control the speed of the setting of the packers by utilizing the timed build-up of gas pressure from the burned flammable solid to force oil through an orifice. The rate of speed is regulated by gas pressure, fluid viscosity, and orifice size. However, the oil is forced through the orifice in response to a build-up of gas pressure from the flammable solid, not in response to other means, such as a hydrostatic pressure of an annulus fluid disposed in a wellbore annulus. The major disadvantage associated with reliance on gas pressure to actuate the tool involves a reduction is gas pressure as the setting tool expands and as the gas cools, thereby reducing setting load. In addition, when the oil is forced through the orifice, there exists no separate selective means in the orifice for initially maintaining the orifice closed thereby preventing the oil from traversing through the orifice and subsequently selectively opening the orifice thereby allowing the oil to traverse through the orifice.